Author Topic: CPC464 corrupted MOBO?  (Read 1201 times)

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Offline gs.davies

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CPC464 corrupted MOBO?
« on: 13:37, 08 October 12 »
Hi, I recently dragged the old 464 which we've had from new (!) out of the shed (!!) and perhaps not surprisingly it no longer works..


It powers up OK, LED is lit, but the display is just a mess of random colours. I can sometimes get the tape deck to start using the CTRL/small ENTER key but not with any kind of reliability. This leads me to believe that it's not a problem with the monitor but with the logic of the machine itself. Perhaps the monitor spiked over 5v DC when I first powered it up?


Any thoughts on what I can do to repair this? I don't believe it's been water damaged, the 'shed' in question is actually very dry, not humid and is in regular use as a summer house.


My seven year old is desperate to see what a bit of vintage computing looks like!


Gary


Offline arnoldemu

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Re: CPC464 corrupted MOBO?
« Reply #1 on: 15:11, 08 October 12 »
welcome Gary.

I wish I could help you to fix this.

My only suggestions are to carefully remove the z80 and put it back in again.

Could you attach a picture to your post?

it sounds like the video is working correctly (6845 and 40010/40007).
Seems like z80's not working correctly..?
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Offline ralferoo

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Re: CPC464 corrupted MOBO?
« Reply #2 on: 16:43, 17 October 12 »
Actually, I'd say the complete opposite. If pressing ctrl+enter works to start up the tape motor, then I'd say that Z80, PPI, PSG, ROM and RAM are all fine.

That pretty much only leaves the gate array or CRTC as being faulty. Can you post a photo of what you see on the screen? If basically, there's a rectangular area full of garbage and a border, then it sounds like the CRTC is fine. If the picture isn't static, then it could well be the CRTC. But a photo of the screen will help diagnose this a lot...

Gary

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Re: CPC464 corrupted MOBO?
« Reply #3 on: 17:49, 26 October 12 »
I'll drag the monitor out over the weekend and rig it up again and snap a picture of the display. It was, from memory, a static mess of random colours. The tape motor started intermittently..
Gary

Offline gs.davies

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Re: CPC464 corrupted MOBO?
« Reply #4 on: 18:03, 26 October 12 »
Just tried it again - each time I switch the machine on I get a different load of coloured garbage on the screen, someimtes bordered and static/nonstatic other times full screen. Most of the time I can't start the tape motor, sometimes the tape motor just starts without a key press...